1. Field of the Invention
The present invention relates to a turbine housing structure of a sheet metal structure, the turbine housing being used for a turbocharger which produces a turbocharged pressure for an engine by use of exhaust gas energy of the engine. The present invention especially relates to the turbine housing structure in which cracks and the like due to thermal stresses are prevented from occurring in a tongue part at a scroll winding end part.
2. Background of the Invention
Conventionally, turbochargers which enhance power output of an engine by supplying a pressurized air into the intake manifold of the engine by use of the exhaust gas energy discharged from the engine are known. When the turbocharger is mounted as a vehicle use, it is required to reduce the weight of the turbocharger especially in view of the tendency regarding fuel consumption improvement in recent years; thus, instead of the conventional turbine housing made by casting, turbine housings made of sheet metal have been used in recent years.
On the other hand, the turbine housing has the function of taking the engine exhaust gas in the housing and making the turbine rotor rotate. Consequently, the exhaust gas of the temperature level of 600 to 1050° C. streams into the turbine housing; a so-called tongue part, namely a gathering area of the gas flow inlet part of a circular shape in the turbine housing and the gas gathering part of the circulated gas flow end, is steeply heated up by the inlet gas flow and the gathering gas flow
When the tongue part is steeply heated up, a force constraining a thermal elongation is generated by the temperature difference between the tongue part and a neighborhood area thereof. Hence, compression thermal stresses are generated. And, there arises a problem that the repeated thermal stresses cause cracks attributable to thermal stresses.
Also in a case of a turbine housing made of sheet metal, there has been a problem that the cracks due to the repeated thermal stresses attributable to the rapid heating of the tongue part are caused. Consequently, it is necessary to use sheet metal of even thickness; further, it is necessary to use sheet metal of thin thickness so that the thermal stress is reduced to the level free from the damage due to the inner pressure.
In addition, as a conventional technology in the related field, the structure of the turbine housing made of sheet metal has been proposed by Patent Reference 1 (JP2008-57448) or Patent Reference 2 (JP_P2003-536009). Further, Patent Reference 3 (JP2002-194525) proposes a structure of the tongue part whose thickness is increased by forming a thick plasma coating in comparison with the areas other than the tongue part, in order to enhance wear resistance property of the tongue part.